Not using magic against Alistair is one thing, sure, but no one had said Anders couldn't let a small thrum of power run through his extremities, warming his hands to keep them from freezing as he balls the snow up. What Alistair doesn't know won't hurt him...

Anders lurches to the side to dodge the snowball Alistair sends streaking toward him; it glances off his shoulder and breaks apart, wet clumps sticking to his shoulder guard. "Child's play! Why don't you try this on for size?"

He cocks his arm back and lets fly with his snowball. He's thrown enough fireballs in his day to have a fair throwing arm, if he does say so himself.